1. Field of the Invention
The present invention relates to systems in which user stations, such as communications terminals in general or telephone sets in particular, are connected in parallel to the same source, but only one can be connected with the source at a given moment. This invention particularly relates to a device for connecting the source and one of the user stations, while excluding any connection of the source with the other stations.
2. Background
There are many systems in which a source of voltage is common to several user stations, but where only one station can be connected to the source at a given moment, excluding the other stations. Such a source can provide direct or alternating current, and digital or analog data; e.g., a telephone line on which several telephone sets can be connected. The connection of many terminals on a common trunk can be done in different ways, of which the simplest is a connection of the stations in parallel. Connection in parallel, however, presents major disadvantages. The telephone line regards the value of the electric parameters divided by the number of the stations placed into parallel. Connection in parallel presents problems of adaptation; moreover, it does not ensure communications secrecy. The stations are always connected simultaneously on the common trunk.
Another solution consists in placing a mechanical reverser in the circuit; in this case there is no problem of adaptation. But the disadvantage of this solution is that it requires human intervention, and when necessary displacement for manipulations. Still another solution consists in installing an automatic reverser containing electromagnetic relays. The miniature relays (which are essential for this solution) may be on integrated circuits, and make it possible to produce perfect switches, but this requires relatively high operating currents. I.e., a relay reverser of 5 volts consumes between 25 and 30 milliamps.